Electronic fuses (e-fuses) are being introduced in DC (Direct Current) power distribution systems for use with various electronic devices. For example, in new RBS (Radio Base Station) models, e-fuses are starting to replace traditional hydraulic-magnetic circuit breakers or fuses. E-fuses allow integration of more functionality and flexibility in the power distribution systems.
A simplified DC system, according to the prior art, comprising a voltage source 505, connected to a surge protective device (SPD) 504 via an e-fuse 301 is shown in FIG. 1. An e-fuse 301 is normally used in conjunction with an SPD 504 when DC-power is supplied from a voltage source 505 to an electronic device (not shown) when exposed to surges on the distribution wiring. The described e-fuse 301 is designed for DC applications and comprises therefore a current path with a predetermined operational DC direction. In the example illustrated in FIG. 1, the operational DC direction corresponds to a clockwise current flow.
The e-fuse of FIG. 1 may be configured according to the simplified scheme of FIG. 2, where the e-fuse 301 comprises a current sensor 500 which is adapted to measure an electric current flowing in the current path. A transistor switch 501 is also located in the current path of the e-fuse 301. In the state of the art e-fuse 301 design, the transistor switch 501 is usually a unidirectional switch based on an N-channel FET transistor. This component typically has a parasitic diode 511 which can be inherent to the semi-conductor device. The parasitic diode 511 is anti-parallel, i.e. its forward direction is opposite to the operational DC direction of the e-fuse 301. The e-fuse 301 as illustrated in FIG. 2 further comprises a controller 502 which is operatively connected to the current sensor 500 and the transistor switch 501. The controller 502 controls the transistor switch 501 based on the measured current. If the measured current is an over current, i.e. a current that exceeds a threshold current, which may be referred to as a security threshold, then the controller is adapted to open the transistor switch 501 in order to interrupt the current flow in the current path of the e-fuse 301.
In many applications, electronic equipment may be subject to sudden current surges, typically caused by lightning. State of the art e-fuses 301 often fail due to incapacity of interrupting a sudden current surge. When feeding electronic equipment exposed to lightning threats, the power distribution and e-fuses 301 must be protected by one or several SPDs 504. The e-fuse 301 should be able to disrupt the surge current and divert the energy to an external SPD 504 and to restore normal operation once the surge condition has disappeared. If the e-fuse 301 fails to disrupt a surge current to an external SPD 504 the e-fuse and the electronic equipment may be exposed currents which may be magnitudes larger than the load current. Consequently, the e-fuse 301 and/or the electronic equipment may in some situations be partly or completely out of service and a repair visit will be necessary.